Torsion damping mechanisms have long been used to reduce the adverse effects of torsionals or fluctuating torques in vehicle drivelines. Such torsionals or fluctuating torques emanate primarily from engine power pulses and torque spikes, and from abrupt changes in driveline torque due primarily to rapid engine acceleration/deceleration and transmission ratio changes. Effective damping of such torsionals has become increasingly more difficult due to current development trends necessitated by a need to improve vehicle efficiency. The need for improved vehicle efficiency has resulted in reductions in vehicle size and weight, reductions in inertia of driveline components such as flywheel masses, reductions in the number of engine cylinders or chambers, reductions in engine speed, increases in the number of transmission gear radios, reductions in transmission oil viscosity, and increased use of torque converter bypass clutches.
These developments have dramatically rattle, as it is sometimes referred to, can be particularly annoying when a manual transmission is in neutral with the input shaft clutched to an engine running at or near idle speed; under this condition low amplitude engine torsionals rattle meshed gears not under load. Body noise or body boom, as it is sometimes referred to, often occurs when an engine is lugged; under such a condition, engine torsionals cause body components, such as sheet metal panels, to resonate. Vehicle jerk, known as tip-in/tip-out, occurs in response to abrupt engine acceleration/deceleration and ratio changes.
The prior art is replete with torsion damping mechanisms incorporated in conventional clutch plates disposed between engine flywheels and transmissions. It is also known to dispose a torsion damping mechanism between primary and secondary flywheel masses as taught by A. Sebulke et al, "The Two Mass-Flywheel", FISTA-Congress, Belgrade, June 1986. The two mass flywheel assembly of Sebulke and Wangung comprises rotatably mounting the secondary mass on the primary mass, helical compression springs interconnecting the masses, and coulomb or mechanical friction surfaces disposed in parallel with the springs and also interconnecting the masses. This two mass flywheel assembly is said to greatly reduce gear rattle since it can be made to operate in the super critical range at all engine speeds above engine idle. However, the two mass flywheel assemblies have required additional damping mechanism to counter damaging low frequency resonance produced during engine starting and stopping. Additionally, the helical compression springs for attenuating torsionals in this two mass flywheel assembly are disposed radially outward further than they would be in a conventional clutch plate. Accordingly, the helical springs and their associated components are subject to increased friction and wear due to higher centrifugal forces and travel. Additionally, axial space limitations in some installations have prevented application of this two mass flywheel assembly due primarily to the helical springs increasing the overall axial length of the assembly.